AG Urban

Stephan Urban
Head of the Hepatitis B Research Group

Phone: +49 (0)6221-56 4902
Fax: +49 (0)6221-56 1946

Development of envelope protein-derived entry inhibitors for the treatment of acute and chronic HBV and HDV infection

Research Team Members

Research Projects

Characterization of viral and cellular determinants essential for HBV entry

Unlike other pathogenic viruses, the initial steps of the hepatitis B virus (HBV) infection, including attachment and receptor recognition, but also subsequent processes, such as the endocytosis pathway, the mechanism of membrane fusion or the intracellular transport events are still unknown. The objectives of this project comprise the deciphering and functional characterization of viral and cellular components that participate in the establishment of the viral infection. A particular focus is related to the identification of host cell factors that function as primary attachment receptors. In this respect we scrutinize the dependence of HBV binding and infection on cell-surface associated glycosaminoglycans. In addition to the visualization of HBV-entry using fluorescently labeld HBV-particles we are trying to dissect the dependence of intracellular sorting and trafficking events on the host cell cytoskeleton.

Identification and analysis of molecular components involved DHBV entry

Early steps in the duck hepatitis B virus (DHBV) life cycle were the subject of many studies in the past. This led to the identification of one receptor component, duck carboxypeptidase D (dCPD/gp180). Although a crucial function for this glycoprotein at some stage of DHBV entry is well established, some features (e.g. preferential TGN localization, binding to the most inner, transmembrane adjacent C-domain, lack of liver specific expression) question the role of CPD as a simple attachment receptor. In this project we aim to elucidate the exact role of CPD during viral binding to hepatocytes and e.g. fusion of viral and cellular membranes. Moreover we are trying to identify components other than dCPD which participate in viral entry. Finally, we are interested in the resolution of the structure of the dCPD domain interacting with the large DHBV surface protein.

Ultrastructural dynamics of Hepatitis B Virus maturation

In the infected cell, newly synthesized genomic RNA is packaged together with the viral Pol-protein and a cellular chaperone complex into capsids. The RNA is then reverse transcribed into a partially double-stranded DNA within the capsid. Under natural conditions, almost exclusively mature capsids containing DNA are enveloped to be secreted as virions. The selectivity of this process depends on a still undefined maturation signal that communicates the RNA-DNA-transition from the interior to the capsid exterior.

The large envelope protein of HBV (L-protein) adopts two transmembrane topologies: At first, its preS-region is located on the cytosolic side of the ER-membrane and acts as a matrix-domain that binds the mature capsid to enable its envelopment. The same region is thereafter required on the viron surface as a receptor binding domain to initiate the next round of infection. So far, it is unknown if the dual topology is already pre-formed prior to viral budding and therefore stably present in the viral particles. Alternatively, the topological switch could proceed mainly in free virions after secretion as a second, distinct maturation step. Using highly purified viral particles, we are characterising the determinants and dynamics of the two proposed maturation steps with biochemical and imaging techniques.

Development of novel entry inhibitors for the treatment of acute and chronic Hepatitis B and Hepatitis D virus infections

Specific inhibition of virus entry into host cells is an established and powerful therapeutic concept to come across acute infections. For chronic infections e.g. HIV, Enfurvitide/Fuzeon®, a peptide inhibitor which prevents fusion of the viral membrane with the lymphocyte membrane has successfully been approved recently. The remarkable in vitro and in vivo inhibitory activity of acylated HBV-preS-derived peptides implies possible clinical applications like prophylaxis of HBV-reinfection after liver transplantation or the protection of newborns from vertical HBV-transmission from their infected mothers. Since it is still unclear to which degree the maintenance of a chronic HBV carrier state depends on constantly ongoing new infection events in the liver (whilst simultaneously infected cells are eliminated by the immune system), entry inhibition might also be an intriguing concept for the treatment of chronic HBV infections.

We are currently performing preclinical studies including the improvement of knowledge on production, efficacy, stability, bioavailability of HBV envelope protein-derived lipopeptides. We are aiming to optimize their in vivo application form and investigate to what extend the immunologic responses contribute to the therapeutic outcome. Aim of these studies is the subsequent accomplishment of a Phase I clinical trial in the near future.